DESCRIPTION: The intent of this grant continuation is to focus on investigating the interface between the resin matrix and the glass filler. X-ray tomography will be used to obtain two-dimensional crack fronts of Dental composite and through image analysis construct three-dimensional representations of the crack surface interface. Also investigated will be the effect of aging in artificial saliva with and without enzymes on the leaching of ions from the glass filler. This will be accomplished using transmission electron microscopy (TEM) with microanalysis. Modeling the micro level stresses and strains in Dental composites will be used to predict the material properties of Dental composites, e.g., fracture toughness, at the macroscopic level. In addition, effects such as environmental loading (in this case artificial saliva and salivary enzymes) and aging (thermal and load cycling) can be modeled at the microscopic level to predict failure patterns of Dental composites under various loading conditions. Finally, a simple chemical model will be prepared and tested by mass spectrometry (MS) to represent the silane coupling agent and its attachment to the resin matrix and the glass filler. This model will also use MS to examine the chemical effect of aging in artificial saliva with and without enzymes. These three Aims are interrelated in that the silane bonding model will be used to help model the microstructure, the ion leaching will be utilized in the micro and chemical model, and the three dimensional crack tomography will be used to validate both models. The Specific Aims of this grant continuation are: 1) To determine the three-dimensional crack path of Dental composites and human teeth using tomography at the Advanced Photon Source at Argonne National Laboratory and to determine the inorganic leached components from the glass fillers using TEM microanalysis; 2) To model microstructural damage and failure of Dental composites; and 3) To correlate the degradation of resin-silane-bonds in Dental composite materials to their fracture during aging.